1. Field of the Invention
The present invention generally relates to the measurement of radioactivity, and, more particularly, to a system and method for measurement of radioactivity concentration of a radiopharmaceutical.
2. Description of the Related Art
Medical imaging is used extensively to diagnose and treat patients. A number of modalities are well known, such as Magnetic Resonance Imaging (MRI), Computed Tomography (CT), Positron Emission Tomography (PET), and Single Photon Emission Computed Tomography (SPECT). These modalities provide complementary diagnostic information. For example, PET and SPECT scans illustrate functional aspects of the organ or region being examined and allow metabolic measurements, but delineate the body structure relatively poorly. On the other hand, CT and MRI images provide excellent structural information about the body, but provide little functional information.
PET and SPECT are classified as “nuclear medicine” because they measure an emission of a radioactive tracer that has been injected into a patient. After the radioactive tracer, or radiopharmaceutical, is injected, it is absorbed by the blood or a particular organ of interest. The patient is then moved into the PET or SPECT detector that measures the emission of the radiopharmaceutical and creates an image from the characteristics of the detected emission.
A significant step in conducting a PET or SPECT scan is the step of acquiring the radioactive tracer. Examples of radiopharmaceuticals include FDG (2-[18F]-fluoro-2-deoxyglucose), other 18F based fluorinated tracers, 13N ammonia, 11C based tracers, 15O gas, and 15O water, and others.
The half lives of these radiopharmaceuticals range from two minutes to two hours. Thus, the injection into the patient and the imaging must take place within a very short time period after production of the radiopharmaceutical. Because of this, it is important for the technician operating the medical imaging device to know the radioactive concentration, as well as the time and date that the radioactive concentration was measured. This may be determined by measuring the total radioactivity of a tracer in an ionization chamber, and taking an aliquot in a syringe to measure the activity concentration. Either the aliquot is put into an ionization chamber or the change of radioactivity of the bulk solution is determined. With the known volume of the aliquot and the measured radioactivity, radioactivity concentration can then be determined.